A guidance system for a Non-Line of Sight (NLOS) weapon system is a missile system which employs a glass fiber optic cable to transmit the signal from the launch site to the missile in flight. A missile system which employs such a signal transmission system is the Fog-M (i.e., fiber optic guided missile). The fiber optic or glass fiber is connected at one end to the missile guidance system and to the signal source at the other end. The fiber optic cable is wound on a bobbin from which the fiber optic payout takes place during missile flight. The signal is transmitted through the wound fiber optic material on the bobbin to link the missile during flight with the signal source.
The glass fiber is produced from a high purity silica preform rod wherein the preform rod is heated to its yield point at about 2000.degree. C., and a fiber is drawn from the heated preform. The manufacturing process must be controlled to produce fibers of uniform diameter and mechanical strength. For example, a mechanical strength of optical fibers in excess of 2.times.10.sup.5 psi is a desirable feature for certain specialized application (e.g., optical waveguides employing lengths of fiber).
Both mechanical strength of the fiber when manufactured and the ability of the fiber to retain its strength when stored are equally important. During storage the loss of mechanical property values can take place in addition to the loss during fiber drawing. Lack of mechanical strength is due to submicron flaws in the surface attributed, mainly, to chemical attack by atmospheric contaminants (e.g., moisture) during and after fiber drawing. Attempts to solve these problems have been studied by applying organic coating to the fiber following the drawing of the fiber. Failure resulted because those organic coatings are not impervious to moisture or hydroxy penetration. The penetration by moisture or hydroxy resulted in reduced strength of the coated fiber during periods of storage and/or use.
U.S. Pat. No. 4,227,907 issued to James A. Merritt and assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C. disclosed a laser photochemical synthesis coating on optical fiber. As described hereinabove, the fiber which is drawn from a heated preform is immediately hermetically sealed with a layer of silicon nitride of about 0.02 to about 0.20 micrometer thickness. The Si.sub.3 N.sub.4 is deposited by laser photochemical reactions which forms the Si.sub.3 N.sub.4 on the freshly drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs the reactant gases, SiH.sub.4 and NX.sub.3, wherein x is selected from hydrogen and/or fluorine.
The drawn fiber optic material when received from the manufacturer is coated with a buffer coat which can be an organic compound (e.g., methyl methacrylate, epoxy acrylates (Desota 95 008), polyimides, polyquinolines, and polsilazanes), or an inorganic compound such as Si.sub.3 N.sub.4. The drawn fiber optic material has a diameter from about 80 to 125 microns or from about 80 to 125 micrometers. The buffer coat when of organic origin adds to this diameter to a total diameter of fiber optic material plus buffer coat to equal about 250 microns. The inorganic coated fiber optical material when coated by the laser photochemical synthesis method increases the diameter by a smaller amount since the coating of Si.sub.3 N.sub.4 ranges from about 0.02 micrometers to about 0.20 micrometers.
An additional requirement for glass fiber coated with a buffer coat prior to being wound on a bobbin is to ensure that the fiber optic materials payout evenly from the bobbin to avoid breakage or malfunction of the fiber optic connection between the missile and the signal source sending the signal.
When winding of optical fiber onto a bobbin from the optical fiber supply spool, the peel angle has now been determined to be critical, although this criticality was not earlier recognized. It was determined during a strength degradation study of the fiber optic cable wound by an engineering developing model (EDM) winder system that the winder imparted unacceptable stress to the fiber optic cable. In efforts to reduce or eliminate the known problems of the EDM system, one of the major and most serious problems was recognized. This most serious problem resulted from the fiber optic cable not entering the winding path at an acceptable angle, and as a result thereof, some twist was transferred to the fiber optic cable. The term fiber optic cable is also used in the art as another description of the fiber wound on a bobbin. Although, very small in diameter as contrasted with the term "cable" as applied to other fields and uses, this description avoids the double use of "fiber" in fiber optic fiber. Therefore, the term fiber optic cable is used interchangeably with fiber optic fiber.
Another problem surfaced during the strength degradation study which relates to the use of mechanical "fingers" that are in constant contact with the fiber to help avoid a "jump" of the fiber optic cable when its peel point from supply spool is at the extreme edge of the path from its present location to its next peel point. This results in an impulse that the tension control system of the winder cannot compensate for. The conclusive opinion based on handling studies indicate that constant contact of mechanical fingers with the fiber greatly increases the chance of fiber failure. The relationship of increased peel angle also results in a certain amount of twist being applied (as earlier noted) to the fiber optic cable. This twist can accumulate in the winding path thereby making the fiber optic cable have a tendency to roll when it is wound onto a bobbin.
The advantages of a non-contact device that regulates the peel angle and which thereby reduces the twist and stress imparted to the fiber optic cable are recognized.
Therefore, an object of this invention is to provide a non-contact device and method for assuring that the fiber optic cable is unwound from a supply spool at a nominal angle to the bobbin on which the fiber optic cable is wound.
Another object of this invention is to provide a device which functions by employing multiple pairs of source and receivers as the control means for proper positioning of a fiber optic cable supply spool to a winder platform to thereby provide a predetermined peel angle of the cable while being unwound from the supply spool and while being wound on a bobbin.